Augmentative biological control of whiteflies using transplants

Field studies showed that transplants can be used to move parasitoids into fields of commercially grown cantaloupe, Cucumis melo (Cucurbitaceae), and augment parasitism of sweet potato whitefly, Bemisia tabaci biotype B (=Bemisia argentifolii) (Homoptera: Aleyrodidae). Methods were developed to inoculate cantaloupe seedlings with newly imported Eretmocerus spp. (Hymenoptera: Aphelinidae), then transfer plants into both organic and conventional fields of cantaloupe in the desert growing region of southeastern California. Several obstacles to inoculating "banker plants" with an adequate number of parasitized whiteflies were overcome and numbers of parasitoids per transplant increased. In 1999 the use of banker plants was compared to a standard hand-release method and a no-release control in a replicated study at an organic farm. Augmentation through releases of parasitoids increased parasitism over that in the no-release controls (p < 0.05). Banker plants increased the proportion of parasitized whiteflies more than the hand-release method (0.21 vs. 0.08). During a region-wide demonstration spring 2000, plots receiving banker plants significantly increased parasitism over paired control plots at seven commercial farms of cantaloupe. Parasitism in banker plant treated plots in 2000 was higher in organic fields (seasonal average = 0.30) than conventional ones (seasonal average = 0.06). Differences may be due to the use of imidacloprid, a systemic insecticide, in conventional fields for whitefly control. Over the 2-year study, however, releases of parasitoids did not consistently reduce densities of B. tabaci. Only in late season at some sites in 2000 were whitefly densities lower in release plots than paired controls. Most of the parasitoids recovered and identified from plots receiving parasitoids were the same as those released, Eretmocerus spp. (ex. Ethiopia M96076), and E. hayati (M95012, ex. Pakistan).